A rain garden is an attractive garden with a special purpose — to improve local water quality and reduce the impacts of storm water on area streams. Communities around the country have experienced dramatic reductions in storm water pollution, due to many homeowners installing rain gardens on their properties. According to the US Environmental Protection Agency (EPA), 70 percent of all water pollution comes from pollutants carried in storm water runoff. A few examples of these pollutants include pet waste, fertilizers, oils and greases from automobiles, and trash (i.e. non-point pollution sources). Rain gardens are effective in removing up to 90 percent of nutrient and chemical pollutants and up to 80 percent of sediments from storm waters flowing into them. This polluted water would otherwise reach nearby streams, rivers and lakes untreated. Not only are rain gardens helpful to water quality, they also create beautiful additions to any landscape and can help reduce localized flooding or standing water in nearby streets. Constructing, installing and maintaining a rain garden will help reduce pollution and flooding, and help keep our local water supplies and recreational areas healthy.
A rain garden is a garden of native shrubs, perennials, and flowers planted in a small depression, which is generally formed on a natural slope. It is designed to temporarily hold and soak in rain water runoff that flows from roofs, driveways, patios or lawns, preventing it from entering the storm sewer system. Soil and plant roots use natural processes to improve water quality by filtering pollutants. Rain gardens are effective in removing up to 90 percent of nutrients and chemicals, and up to 80 percent of sediments from the storm water runoff. Compared to a conventional lawn, rain gardens allow for 30 percent more water to soak into the ground. The water is held by the garden and allowed to slowly infiltrate the soil, providing an important role in recharging ground water supplies and reducing storm water runoff volumes to local streams. A rain garden is not a pond or wetland, but is dry most of the time and typically holds water during and following a rainfall event (usually not more than two days).
A rain garden is bowl or saucer shaped, not mounded or flat like other perennial gardens. Like a conventional garden, a rain garden is a beautiful form of landscaping; however, a rain garden also is designed with deep, loose soil specifically to collect and absorb rain that would otherwise run off your property, and/or to solve wet spot problems where water already is collecting.
In the design of a rain garden, typically 6 to 12 inches of soil is removed and altered with tillage, compost and sand to increase water infiltration. The type of alteration to the soil depends on the current soil type, so it is a good idea to conduct a simple test of your soil’s infiltration rate. See design guidance tab for soil testing information.
Instead of using cultivated plants from Europe and Asia, a rain garden is planted primarily with deep-rooted, low-care, perennial plants native to your region, that have adapted over thousands of years to your local weather and conditions. The deep roots provide channels into your soil, into which water may travel. The native plants provide habitat for local butterflies and other wildlife. The native plants do not need to be treated with chemical fertilizers, insecticides or herbicides in order to thrive.
• Improves water quality by filtering out pollutants
• Provides localized storm water and flood control
• Easy to maintain after establishment
• Preserves and promotes native vegetation
• Attracts beneficial birds, butterflies and insects
• Provides aesthetically pleasing landscaping
• Provides a storm water management solution for homeowners who properly disconnect their downspouts from the sanitary or combined sewer system
We tend to think that large industrial polluters cause most water pollution, but this is not the case. We are the real culprits. The EPA has determined that up to 70 percent of the pollution in our surface waters is carried there by storm water runoff. Some studies show that about 50 percent of that pollution comes from individuals and homeowners due to yard care, yard waste and chemical pollution from household activities. When it rains, water runs off of our roofs, parking lots, streets and lawns, instead of soaking into the soil the way it did before development. This water, along with everything it picks up along the way, ends up in storm sewers and ditches that discharge to streams, rivers and lakes. Salt from roads, bacteria from pet waste, lawn nutrients, spilled gas, oil and other pollutants are all washed into local waterways. Most modern American cities are built in such a way that when it rains, all of the water is directed into storm sewers via gutters, curbs and ditches, and then the water flows directly into nearby creeks and streams.
In addition to carrying pollution, the storm water runoff is usually warm, causing a pulse of warmer water to flow down the stream. In a natural system, water enters a stream through a slow and steady release from groundwater. Groundwater has a fairly cool temperature, which allows water to hold more oxygen and keeps stream habitat stable. Many sensitive creatures, such as trout, cannot survive in a stream with fluctuating and warmer temperatures. While groundwater release is slow and fairly steady, storm water runoff occurs all at once. The large volumes of warm water flushing downstream cause erosion and flooding, carry dam-forming debris, and scour the stream bed.
An impervious surface is any surface that doesn’t allow rain water to penetrate into the soil, including roofs, roads, cement or gravel driveways, sidewalks, and most lawns (because the shallow, dense root system acts almost like cement). Impervious surfaces contribute to increased amounts of storm water runoff, increased non-point water pollution, and the urban heat island effect.
• Plant native plant gardens in your yard
• Reduce the overall amount of concrete on your property
• Consider alternative materials for patios and new driveways such as permeable pavers or pavement
• Construct a rain garden to collect storm water from your roof and driveway
No, not if properly constructed. Rain gardens are designed to absorb water, not to create ponds. Properly installed, your rain garden will not hold water long enough for mosquito larvae to complete their 7-to-12-day life cycle. A well-designed rain garden with mature plants will not have standing water in it after 48 hours; all the water will have soaked into the garden. In fact, rain gutters on homes are much more likely to produce mosquitoes than a rain garden.
Fragrant flowering plants do attract a wide variety of birds and bees. Remember that 90 percent of insects are beneficial to gardening and rest assured that rain gardens are filled with busy pollinators pursuing nectar.
No. Rain gardens do have a natural rather than a manicured appearance, but they need not look messy. You can keep a rain garden looking neat and attractive by keeping the edges well defined. Taller plants often have a more unkempt appearance; so use shorter plants if you want your garden to have a cleaner look.
Rain gardens are designed to infiltrate water in about one day. If it rains several days in a row, it is possible that your rain garden may have standing water until the rain stops and the water has time to soak in. If designed and installed correctly, rain gardens typically do not have standing water for more than 48 hours. Be sure to test the soil type and infiltration rate, or percolation rate, before beginning your rain garden. Rain gardens may not be appropriate for all locations; high water tables, clay soils and bedrock locations may inhibit infiltration.
Rain gardens are designed to hold water for no more than a couple of days. Unlike ponds, you don’t need costly pumps, electricity or filters. In fact, a rain garden is a filter for the water that runs off of your property’s impervious surfaces.
During storms, rain gardens can fill with standing water but the typical amount of water is no more than 18 inches. This water will begin to recede immediately after the rain has stopped, emptying in a matter of minutes or hours. If standing water is a concern, you may add a few inches of pea gravel. See design guidance tab to find different cross section alternatives.
A rain garden should have an area about 20 percent the size of the roof, patio or pavement area draining into it. A typical residential rain garden is between 100 and 300 square feet. If a smaller rain garden than recommended for a lot is chosen by the landowner, the garden will still function. Any size rain garden can make a positive impact by infiltrating some storm water. A Calculator is available at the design guidance tab to assist with sizing your rain garden. Or, simply seek help from a landscaper or other professional. Rain gardens can vary in size and complexity depending on your site constraints and how you would like it to function. See design guidance tab for different types of rain garden design.
Rain gardens are generally constructed on the downside of a slope on your property to collect natural drainage and runoff from your lawn, roof and driveway. The easiest way to read the slope and drainage of your yard is to watch water when it is raining. Take a few pictures to help you remember where water goes during and after a rainfall event. In a low area of your yard, a complex mix of plants and soil will absorb a lot of rain.
Rain gardens are typically designed longer than they are wide and are perpendicular to the slope, in order to catch the maximum amount of rainfall. Rain gardens should be placed at least 10 feet away from building foundations. Generally you should avoid utility rights of way, where gas, phone and telephone lines are located. Also keep the garden location away from septic drain fields, which don’t need any extra water.
Since the plants are aesthetically pleasing and attract birds and butterflies, locating a rain garden outside a picture window can provide the benefit of indoor enjoyment. On hot days in summer, many hummingbirds will be attracted to the plants of a rain garden. Every garden is site specific and unique; you can make it what you want to make it.
The best drainage will occur in full sun; however, many plants can be chosen to thrive in a part sun/full shade rain garden as well (see shade planting plan). The water will take a little longer to be absorbed, but the garden will function well in any sun exposure if the right plants are used.
Yes, but choose clay-loving plants and amend your soil. Typically, 6 to 12 inches of soil are removed and altered with tillage, compost and sand to increase water infiltration and allow for more plant diversity. The type of alteration to the soil depends on the current soil type (clay content), so it is a good idea to obtain a soil test. See our soil supplier lists for amended soil materials and guidance. Ask one of our plant supplier experts for plant selection advice.
Customized planting plans are available here. A list of plant and soil suppliers is also available here.
They can be simple—just a green area of your yard where storm water goes—or complex, involving excavating and re-building soil. They also may be “industrial strength,” handling large volumes of water periodically, where large-scale storm water management regulations must be met.
Yes. See our designs and construction information. Although it may take a little more digging to create the depression, rain gardens are no harder to install than a traditional perennial garden. If you need some help or just a little encouragement, check out the Resource page and Partners page.
Check our contact information for local resources in the “Where Can I Find” section of the website for the names of local landscape architect firms or look in the Yellow Pages under Landscape Architects or Landscape Contractors. Remember that not all landscapers are experienced in building rain gardens, so ask lots of questions to be sure you’re hiring someone who will build you a quality rain garden.
While drain tiles are not required for most rain garden projects, some homeowners want to direct drainage across or beneath a lawn to the rain garden. In this case, most home improvement stores stock drain tile. Drain tile is simply a flexible plastic hose that resembles an underground gutter. See materials supplier section for more information.
Organic mulch is recommended for formal rain garden designs. Mulch keeps the garden moist and able to absorb rain, makes the garden look tidy, and discourages weeds. An application of hardwood mulch will look good, and compost mulches will enrich the soil. Large rain gardens or bioretention systems that are planted from seed are not mulched.
The cost of a rain garden is dependent on the property’s soil type, the size of roof, driveway, and patio draining into a rain garden, and the types of plants chosen. If the soil is high in clay content, the garden may require adding a soil amendment to prevent standing water for more than 48 hours. For a self-built rain garden, expect to pay between $3 and $7 per square foot in plant costs and soil amendments. Digging the garden is the most time consuming task, as a depression needs to be created to catch the water and often 6 to 8 inches of additional soil depth is typically removed to add soil amendments. When working with a landscaping company to design and install a rain garden, the cost will significantly increase to around $10 to $15 per square foot. Plants are the single most expensive item so if you have friends or neighbors with native plant beds, consider asking them to split and donate some of their “good producers.” Remember, an important cost consideration is that like other perennial flower gardens, rain gardens are less expensive than replanting annuals every year.
If native plants are used, rain gardens require less maintenance than a conventional garden They adapt well to their natural surroundings, and do not need fertilizers or pesticides. During the first few years after the installation of a rain garden, the weeds will need to be removed periodically. After the plants in the rain garden are well established and have grown larger, they will eventually out-compete the weeds. During the first and second year, or during periods of little to no rainfall, occasional watering of the plants will be necessary.
Though many native plants were subject to burns, cutting to the ground in winter mimics the “burn cycle” and encourages growth for the next year. So consider this strategy for your rain garden if you want to encourage wildflower and forb growth. However, consider that brown, dry seed heads can provide important bird food over the winter.
No, many natives are not aggressive. In fact, many are struggling to compete with non native plants in the wild, so providing a habitat for them is good stewardship. Ironically, one challenge will be to keep turf grass species out of the rain garden. Choose rain garden plant varieties that are not aggressive and mow the area around the garden. NOTE: many native plants are highly sensitive to tiny traces of weed killers. You may see curling and damage to your new plants if you or a nearby neighbor sprays weed killer.
If at all possible, avoid placing the rain garden near a mature tree. Roots, seeds and shade are challenges, but you can work with these if you make good choices. Try to stay flexible when digging, as roots may cause you to re-route a bit. You may need to keep up on weeding the seedlings more frequently, and you should choose shade-loving plants.
As a rule, native vegetation should be incorporated into a rain garden. Native plants don’t require fertilizer, have good root systems, and are better at utilizing the water and nutrients available in their native soils than non-native species. Perennials, shrubs, wildflowers, or a mixture of all three can be planted. Avoid planting trees, as trees generally absorb more water than surrounding plants. We recommend species native to your region, but other cultivated non-native species can be very beautiful, too. Also, never plant invasive or noxious species in a rain garden, such as purple loosestrife. See our plant information area for specific information and plant lists and a list of common noxious/invasive species.
Despite what you may think, rain gardens don’t have to be planted with water-loving plants. Since rain gardens drain so quickly (ideally between 24 and 48 hours), the plants you put in only have to be able to tolerate lots of water for brief periods. They also need to be able to withstand periods of drought. Different areas of your garden can be planted with different kinds of plants as well. For example, the area near the top of the depression won’t be receiving as much water as the low-lying middle. If you’re not an experienced gardener or don’t have a lot of experience with native plants, just ask your local native plant nursery for suggestions or ask for technical help. Remember to consider plant height, wildlife attraction, flowering, and sun and shade tolerance when choosing your plants.
Native plants are ideal for landscaping for many reasons. Because they have adapted to Indiana’s climate over millions of years, they don’t need chemicals to help them grow, can tolerate our cold winters and hot summers, have very deep roots that allow them to be more drought resistant, have developed defenses against harmful native insects, and can serve as habitats for native wildlife (consider planting for butterflies, hummingbirds or songbirds). The deep roots of native plants also make them ideal for rain gardens because they create channels in the soil which allow water to soak in quickly (see diagram below to compare the root depths of some native versus non-native species)
You don’t have to use plants native to Indiana, but there are many advantages. Natives have adapted to our climate and are much better at handling the periodic inundation of water that goes along with a rain garden. They’ll also save you the time and money of replanting every year, and will offer much greater wildlife value. Be careful not to plant non-native plants known to be invasive. Invasive species can crowd out and out-compete native species creating a monoculture of one type of plant and potentially spreading into nearby native plant areas creating a habitat problem for local wildlife. First always check the list of common noxious/invasive species invasive plants for Indiana.
Some rain garden plants are carried by many local perennial nurseries, as native species are becoming more popular for home and commercial gardening. Other rain garden plants can be purchased from native plant nurseries. Check our “Where Can I Find” area to locate sources. You may also choose to transplant some suitable plants in your yard, or you could get divisions from a friend.
Large quantities of rain garden plants must be ordered far in advance, as suppliers do not usually keep them on hand unless they have a ready market for them.
Please do not collect your rain garden plants from wild populations. They may be growing everywhere, but they soon won’t be if they are removed from the local landscape. Purchase your plants from a reputable nursery that produces them in a sustainable way.
Yes, many rain garden plants are both beautiful and nutritious for hummingbirds, butterflies, bees and more. Visit our Web site for a planting plan customized to attract birds and butterflies.
Yes, some natives are sweetly fragrant. These often attract a vast array of wildlife (including humans). Visit our Web site for plant lists and descriptions.
Yes, but this will decrease the efficacy and depth of roots for infiltration. Many beautiful flowers depend on shorter grasses for support and nutrient uptake as well. We call these companion grasses. Some are short and provide a lot of visual interest by turning autumn colors and moving softly in a breeze.
Most rain gardens look like a perennial garden and have neat edges that are mowed or trimmed, which gives the appearance of a neat and intentional garden. The owner will need to stay on top of weeding in the first few years especially. Plants with shorter heights can also be selected to produce a more manicured look. Likewise a garden with fewer species may also result in a more manicured look. Visit our Web site for custom planting plans.
Maybe, but only if the weather is very dry for extended periods of time (greater than a month). The amount of water your rain garden needs will depend on the plants you choose. Native plants are adapted to a wide range of conditions, so they will only need watering in the driest seasons. Drought tolerant plants need to grow deep roots during the first two years to withstand dry periods. Overwatering may discourage this important growth. Those that are used to having their “toes” wet should be placed in the lowest part of the garden. Plants that like drier soil are placed on the banks of the garden and can withstand some wet and very dry conditions.
Native plants do not need special attention once they are established. They do not need to be fertilized or sprayed. Storm water carries many nutrients and therefore rain gardens are already fertilized regularly. One benefit of rain gardens is they help remove or take up excess nutrients/fertilizers in storm water. Fertilizing them with additional fertilizer would defeat the garden’s purpose as a storm water treatment method.
No, not if they are properly located and designed. Rain gardens should be located at least 10 feet away from buildings so that water does not drain along foundations. Also, your rain garden should drain away from buildings rather than toward them, so place the garden in the landscape accordingly.
Rain gardens are designed to hold water for no more than a couple of days. Unlike ponds, you don’t need costly pumps, electricity or filters. In fact, a rain garden is a filter for the water that runs off of your property’s impervious surfaces. Rain gardens are very short-term water storage features, and therefore are not conducive to fish.
Amphibians will live in your rain garden if they are provided a chance to burrow down in the ground beneath the garden. Using a liner will deter them from living in your rain garden. Adding a long stick and/or stones for access in and out of puddles will facilitate tiny amphibian and dragonfly activity. These species eat mosquito larvae and adults in and around your yard that may be breeding in gutters or other standing water sources.
Because plants are dormant, their activity is reduced, but the rain garden will still help slow down water movement and enable it to be absorbed into the ground in the winter. The ponding area provides storage for a certain amount of runoff even if the ground is frozen. Water may remain longer, particularly when the ground is frozen, but that’s not a problem in winter. Rain gardens do work best in the spring and summer, but that is when they are most needed to protect streams from polluted runoff and heavy storm volumes. If you leave seeds up or add a feeder, you will see cardinals, finches and other winter birds frequent your yard seeking the important winter nutrition your rain garden plants can provide.
You can place a small amount of snow on your rain garden, but a large amount may compact the soils in the garden or damage the plants. A glacier on the garden in early spring may slow down the greening of your plants. It is better to place large amounts of shoveled snow next to the rain garden; as it melts, it will flow in and be absorbed.
It is better to locate the rain garden away from direct salt discharge. There are some salt-tolerant plants that you might use if the only place you can locate the rain garden will be subject to salt spray and runoff from streets and sidewalks. For large parking lot and street applications, pre-treatment structures may be helpful, such as a sediment settling area. For larger rain gardens for commercial parking lots, an underdrain system would be best; the salty runoff is filtered through the rain garden, then carried away by the underdrain system. This prevents possible groundwater contamination with chlorides.
A sign does a world of good in communicating to neighbors and onlookers. If you are within the city limits of Indianapolis, you can register your rain garden with the City of Indianapolis and elect to receive a sign for your yard. Among other programs, the National Wildlife Federation has a certification and sign program. Installing a rain garden with native plants and leaving the seeds over winter covers the checklist requirements for backyard habitat. To learn more, go to http://www.nwf.org/gardenforwildlife/signOrder.cfm .
In heavy rain events, this may occur. Spring and fall events also can provide repeated filling and delays in drainage. A few solutions to this problem:
• Expand the garden to include the “high water mark.” This is the area your garden “claimed” during the heavy rain.
• Add another rain garden down slope of the first one
• Decrease the amount of downspouts directed into the garden. Our rooftops can produce large quantities, and the rain garden may be too small to accommodate the amount of water you have routed to it.
• Wait until there is a dry spell and dig it deeper. Adding 1 or 2 inches of depth over 5 feet might accommodate enough of the excess water.
• Install a small overflow drain by placing a short length of your drain tile in a high part of the garden. This allows overflow to run off, but only when the garden has filled.
The mulch is showing you where high water levels are. You can expand the garden, or just rake it back into place until the plants are dense enough to keep the soil and mulch in place. If it bothers you, you may wish to add boulders, stones or some large edging like pavers. These will increase the cost and maintenance, but they can be beautiful and functional.
During repeated rain events, the water may drain more slowly in the garden, which is not necessarily a problem. Rest assured that you are filling an important need by restoring the water table slowly. That said, even flooding is not necessarily a problem for your established rain garden. If it becomes an issue, you may wish to accommodate more water by:
• Expanding the garden (width and/or depth).
• Further amending the soil (especially if you have heavy clay soil).
• Adding more wetland sedges and grasses that speed up water use.
Gardening with native plants is not the same as traditional gardening. Remember the goal is to provide a dense vegetative cover that looks beautiful and treats storm water runoff. You can choose varieties that stay put, or you can let the plants choose where they flourish. If you feel you need to remove seeds of varieties that replant via seeds, simply cut off the seed heads once flowering is complete.
This is an excellent opportunity to see storm water in action. Water from the drain tile can have a lot of pressure, so you may need to do one or more of the following:
• Place a block or flat stone under the washed out area. This will help spread the flow to a wider pattern until it fills up.
• Let that area be a deeper point in the garden and move the sediment to higher parts of the garden.
• Keep leaf litter and asphalt debris out of the basin.
• Occasionally reposition the drain tile, allowing it a lot of room for erosion.
There may be a rain garden near you. Check in our regional directory. There are several demonstration rain gardens around the city and within the Upper White River Watershed for you to visit. Consider registering your rain garden with the City of Indianapolis.
If there is a similar project in your area, you may find their information in our regional directory.
Rain gardens and rain barrels essentially serve the same purpose which is reducing the amount of storm water that runs off of your property. A rain garden does this by capturing the water and allowing it to infiltrate into the soil right there on site. A rain barrel on the other hand offers other options for how the water can used. Since storm water contains no chlorine, lime or calcium, and fewer sediments and dissolved salts than municipal water, it is perfect for watering vegetable gardens, raised planter beds and containers, or indoor tropical plants like ferns and orchids. Storm water is perfect for automobile washing and cleaning household windows. Most rain barrels come equipped with faucets for attaching garden hoses. Visit the Sustain Indy Web site to learn more about buying or constructing a rain barrel.